1. Field of the Invention
The present invention relates to a projection optical system enlarging and projecting a modulated light which has been emitted from a small-size image display panel and an image display apparatus including the projection optical system.
2. Description of the Related Art
A projection type (rear-projection type) image display apparatus is known as a scheme to realize a large-screen image display apparatus at low cost. However, there is a problem that such a projection type image display apparatus requires a space for a projection optical path, thereby a depth and a height of the apparatus increase. As improvement schemes for this, it is proposed that a projection light from a projection optical system which includes a lens system and a power mirror is projected onto a projection surface (a screen surface) not vertically but obliquely, thereby a depth size or a height size of the apparatus are reduced.
For example, Japanese Patent Kokai Publication No. 2007-323047 as Patent Document 1 (FIG. 4, FIG. 5 and so on) describes that a modulated light emitted from a lens system is bent by a plane mirror in a horizontal direction before entering a power mirror, thereby reducing a depth size of an image display apparatus.
Further, Japanese Patent Kokai Publication No. 2007-94405 as Patent Document 2 (FIG. 2, FIG. 4 and so on) describes that a modulated light emitted from a lens system is bent upward by a plane mirror before entering a convex mirror, thereby an image display apparatus is reduced in depth size and height size.
However, in conventional projection optical systems, a light flux is always in a state of divergence in an optical path after an emission from a lens system to an incidence on a convex mirror. For this reason, there is the following problem: in order to arrange so that a modulated light after the emission from the lens system to the incidence on the convex mirror does not interfere with another element (e.g., a bottom end of a screen), it is required to provide a large space in a lower part below the screen in the image display apparatus, and thus a height size of the image display apparatus cannot be sufficiently reduced (a height of the lower part below the screen).
A projection optical system of the image display apparatus described in the Patent Document 1 has the following problems that: because the modulated light which is emitted from the lens system and enters the power mirror widely diverges, the plane mirror for bending the modulated light is very large in size. In order to arrange the large plane mirror so as not to interfere with the modulated light which travels from the power mirror to a screen, a large space is required in a lower part below the screen in a housing of the image display apparatus and the image display apparatus cannot be sufficiently reduced in height size (a base-portion-height of the lower part below the screen).
A projection optical system of the image display apparatus described in the Patent Document 2 has the following problems that: because the modulated light which is emitted from the lens system and enters the convex mirror diverges, the plane mirror for bending the modulated light is large in size; and because of the structure that the modulated light is bent upward by the plane mirror, the image display apparatus cannot be sufficiently reduced in height size (a height of a lower part below a screen).